In various multistage rotary machines used for energy conversion, such as turbines, a fluid is used to produce rotational motion. In a gas turbine, for example, a gas is compressed in a compressor and mixed with a fuel source in a combustor. The combination of gas and fuel is then ignited for generating combustion gases that are directed to turbine stage(s) to produce the rotational motion. Both turbine stage(s) and compressor have stationary or non-rotary components, e.g., vanes, that cooperate with rotatable components, e.g., rotor blades, for compressing and expanding the operational gases.
Any fluid leakage between stages reduces turbine performance and efficiency and therefore, interstage seals in seal housings are provided to reduce such leakage. In general, fluid leakage is reduced when the gap between the seal and a rotor assembly is minimized. It is known that during turbine transients, the rotor assembly expands radially and may actually contact the seal, causing undesirable deformation and wear thereof. In order to prevent this undesirable contact from occurring, the seal housing may be positioned at a sufficient distance from the rotor assembly so as to allow for this initial expansion of the rotor assembly. However, during steady state operation, due to the initial positioning of the seal housing, the distance between the seal and rotor assembly may not be optimal for avoiding or reducing leakage of fluid, thus reducing turbine performance.
In view of the foregoing considerations it is desirable to provide a reliable and low-cost arrangement whereby the seals may be positioned closer to the rotor assembly during steady state operation to reduce fluid bypass and to thereby increase the overall efficiency of the rotary machinery. It is further desirable for the seal arrangement to sufficiently and consistently open up during transient periods such as during start up of the turbine or upon turbine shut down in order to prevent undesirable rubbing between the seal and any moving component.